The present invention relates to a stencil printer operable with a master wrapped around a print drum and more particularly to the structure and operation of an ink feeding mechanism included in a stencil printer.
Generally, a thermal digital stencil printer includes a rotatable print drum made up of a porous cylindrical support and a plurality of metallic mesh screens covering the support in a laminate. A stencil to be wrapped around the print drum as a master has a laminate structure consisting of a thermoplastic resin film which is usually 1 .mu.m to 3 .mu.m thick, and a porous substrate to which the resin film is adhered. The substrate is formed of fibers of Japanese paper or synthetic fibers or a mixture thereof. After a thermal head has selectively perforated, or cut, the film surface of the stencil, the resulting master is wrapped around the print drum. Subsequently, ink feeding means arranged within the print drum feeds ink to the inner periphery of the print drum. A press roller or similar pressing means presses a paper or similar recording medium against the print drum with the intermediary of the master. As a result, the ink is transferred to the paper via the porous portion of the drum and the perforations of the master, forming an image on the paper.
A problem with the above stencil printer is that if the ink exists in the print drum in an excessive amount, it leaks from the drum and brings about defective printing. Another problem is that when the printer is not used over a long period of time, the ink is degenerated due to the evaporation of water held in the cylindrical support and mesh screens of the print drum. As a result, when the printer is operated for the first time after such a long time of suspension, it is likely that images are blurred or otherwise effected and causes several to several tens of papers to be wasted.
To solve the above problems, Japanese Patent Laid-Open Publication No. 8-142474, for example, discloses ink collecting means disposed in the print drum and contacting the inner periphery of the drum for collecting excess ink existing in the drum. The ink collecting means, however, constantly contacts the inner periphery of the print drum and produces noise ascribable to friction between the former and the latter. This, coupled with the fact that the ink collecting means collects the ink more than necessary, lowers image density. In addition, the ink collecting means deteriorates rapidly.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 3-164287, 4-296585, 6-135114, 7-52518, 8-25781, and 10-217595.